When I was ten years old, I took a water oriented lifesaving course. The first lesson was about protecting yourself first. You can't help anyone when your own safety is in jeopardy.
Somehow, there has to be a balance between how much you can give and how much is reasonably expected of a sibling, or any family member for that matter.
Tough love is just that - tough!
Also, a change of perception may allow you to realize that it can always be worse. Nirvana is only a fantasy!
Take care of YOU!
Steve